Discovery of a series of ester-substituted NLRP3 inflammasome inhibitors.

The NLRP3 inflammasome is a component of the innate immune system involved in the production of proinflammatory cytokines. Aberrant activation by a wide range of exogenous and endogenous signals can lead to chronic, low-grade inflammation. It has attracted a great deal of interest as a drug target due to the association with diseases of large unmet medical need such as Alzheimer's disease, Parkinson's disease, arthritis, and cancer. To date, no drugs specifically targeting inhibition of the NLRP3 inflammasome have been approved. In this work, we used the known NLRP3 inflammasome inhibitor CP-456,773 (aka CRID3 or MCC 950) as our starting point and undertook a Structure-Activity Relationship (SAR) analysis and subsequent scaffold-hopping exercise. This resulted in the rational design of a series of novel ester-substituted urea compounds that are highly potent and selective NLRP3 inflammasome inhibitors, as exemplified by compounds 44 and 45. It is hypothesized that the ester moiety acts as a highly permeable delivery vehicle and is subsequently hydrolyzed to the carboxylic acid active species by carboxylesterase enzymes. These molecules are greatly differentiated from the state-of-the-art and offer potential in the treatment of NLRP3-driven diseases, particularly where tissue penetration is required.

STAT1 regulates macrophage number and phenotype and prevents renal fibrosis after ischemia-reperfusion injury.

Renal ischemia-reperfusion injury (IRI) leads to acute kidney injury or delayed allograft function, which predisposes to fibrosis in the native kidney or kidney transplant. Here we investigated the role of the signal transducer and activator of transcription 1 (STAT1) in inflammatory responses following renal IRI. Our study showed that a subsequent stimulation of Janus-activated kinase 2/STAT1 and Toll-like receptor 4 pathways led to greater STAT1 activation followed by increased cytokine transcription compared with single-pathway stimulation in murine renal tubular cells. Moreover, we observed increased activation of STAT1 under hypoxic conditions. In vivo, STAT1-/- mice displayed less acute tubular necrosis and decreased macrophage infiltration 24 h after renal ischemia. However, investigation of the healing phase (30 days after IRI) revealed significantly more fibrosis in STAT1-/- than in wild-type kidneys. In addition, we demonstrated increased macrophage infiltration in STAT1-/- kidneys. Flow cytometry analysis revealed that STAT1 deficiency drives an alternatively activated macrophage phenotype, which is associated with downregulated cluster of differentiation 80 expression, decreased intracellular reactive oxygen species production, and enhanced ability for phagocytosis. Furthermore, we detected immunohistochemically enhanced STAT1 expression in human renal allograft biopsies with no interstitial fibrosis/tubular atrophy (IF/TA) compared with specimens with severe IF/TA without specific etiology. Thus, STAT1 activation drives macrophages toward an alternatively activated phenotype and enhances fibrogenesis indicating a potential STAT1-driven protective mechanism in tissue repair after ischemic injury.

STAT2/IRF9 directs a prolonged ISGF3-like transcriptional response and antiviral activity in the absence of STAT1.

Evidence is accumulating for the existence of a signal transducer and activator of transcription 2 (STAT2)/interferon regulatory factor 9 (IRF9)-dependent, STAT1-independent interferon alpha (IFNα) signalling pathway. However, no detailed insight exists into the genome-wide transcriptional regulation and the biological implications of STAT2/IRF9-dependent IFNα signalling as compared with interferon-stimulated gene factor 3 (ISGF3). In STAT1-defeicient U3C cells stably overexpressing human STAT2 (hST2-U3C) and STAT1-deficient murine embryonic fibroblast cells stably overexpressing mouse STAT2 (mST2-MS1KO) we observed that the IFNα-induced expression of 2'-5'-oligoadenylate synthase 2 (OAS2) and interferon-induced protein with tetratricopeptide repeats 1 (Ifit1) correlated with the kinetics of STAT2 phosphorylation, and the presence of a STAT2/IRF9 complex requiring STAT2 phosphorylation and the STAT2 transactivation domain. Subsequent microarray analysis of IFNα-treated wild-type (WT) and STAT1 KO cells overexpressing STAT2 extended our observations and identified ∼120 known antiviral ISRE-containing interferon-stimulated genes (ISGs) commonly up-regulated by STAT2/IRF9 and ISGF3. The STAT2/IRF9-directed expression profile of these IFN-stimulated genes (ISGs) was prolonged as compared with the early and transient response mediated by ISGF3. In addition, we identified a group of 'STAT2/IRF9-specific' ISGs, whose response to IFNα was ISGF3-independent. Finally, STAT2/IRF9 was able to trigger an antiviral response upon encephalomyocarditis virus (EMCV) and vesicular stomatitis Indiana virus (VSV). Our results further prove that IFNα-activated STAT2/IRF9 induces a prolonged ISGF3-like transcriptome and generates an antiviral response in the absence of STAT1. Moreover, the existence of 'STAT2/IRF9-specific' target genes predicts a novel role of STAT2 in IFNα signalling.

Microvascular dysfunction in the course of metabolic syndrome induced by high-fat diet.

BACKGROUND: Metabolic syndrome (MetS) is associated with increased risk of cardiovascular disease (CVD). One important feature underlying the pathophysiology of many types of CVD is microvascular dysfunction. Although components of MetS are themselves CVD risk factors, the risk is increased when the syndrome is considered as one entity. We aimed to characterize microvascular function and some of its influencing factors in the course of MetS development. METHODS: Development of MetS in C57BL/6 mice on a high-fat diet (HFD, 51% of energy from fat) was studied. The initial phase of MetS (I-MetS) was defined as the first 2 weeks of HFD feeding, with the fully developed phase occurring after 8 weeks of HFD. We characterized these phases by assessing changes in adiposity, blood pressure, and microvascular function. All data are presented as mean ± standard error (SEM). Differences between cumulative dose-response curves of myograph experiments were calculated using non-linear regression analysis. In other experiments, comparisons between two groups were made with Student's t-test. Comparisons between more than two groups were made using one-way ANOVA with Tukey post-hoc test. A probability value <0.05 was considered statistically significant. RESULTS: I-MetS mice presented with weight gain, blood pressure elevation, and microvascular dysfunction characterized by augmented vasoconstriction. This finding, contrary to those in mice with fully developed MetS, was not associated with endothelial dysfunction, insulin resistance, or systemic inflammation. In the initial phase, perivascular adipose tissue showed no sign of inflammation and had no influence on the pattern of vasoconstriction. These findings suggest that the onset of hypertension in MetS is strongly influenced by vascular smooth muscle cell dysfunction and independent of important factors known to influence microvascular function and consequently blood pressure levels. CONCLUSION: We identified in I-MetS the occurrence of isolated augmented vasoconstriction along with blood pressure elevation, but not the presence of classical MetS components known to influence microvascular function. These findings increase our understanding of the pathophysiology of CVD risk associated with MetS.

Variability of cognitive performance during hemodialysis: standardization of cognitive assessment.

BACKGROUND/AIMS: Up to 70% of hemodialysis patients over the age of 54 have relevant cognitive impairment. No standardized protocol for the evaluation and monitoring of this population is available today. We hypothesized that the dialysis procedure and the testing environment induce fluctuations of cognitive performance. METHODS: 26 hemodialysis patients were randomly tested using the Montreal Cognitive Assessment (MoCA) before, during and after hemodialysis and inside the dialysis room or alone in a separate room. Tests were performed at weekly intervals using five test variations to prevent learning effects. The Mini-Mental State Examination (MMSE) was performed as a reference test. RESULTS: MoCA scores significantly differed between the conditions: 'before hemodialysis' revealed the best MoCA score as compared to 'during hemodialysis' or 'after hemodialysis' (p = 0.013). During the combined condition 'before dialysis AND separate room', best performance was achieved (p < 0.001). The BP decline had no significant influence on cognitive performance, whereas the fluid shift showed a significant impact (p = 0.008). CONCLUSION: Cognitive performance in hemodialysis patients highly depends on the time point and testing environment. Therefore, we strongly suggest a standardization, using the MoCA before hemodialysis in a separate room, in order to make testing results of future research in this field comparable.

STAT1-mediated signal integration between IFNγ and LPS leads to increased EC and SMC activation and monocyte adhesion.

Inflammation plays an important role in host defenses against infectious agents and injury, but it also contributes to the pathophysiology of atherosclerosis. Signal transducer and activated transcription 1 (STAT1) has been identified as a point of convergence for the cross talk between the pro-inflammatory cytokine interferon γ (IFNγ) and the Toll-like receptor-4 (TLR4) ligand LPS in immune cells. However, there is no information available on the role of STAT1 in TLR4-mediated progression of atherosclerosis and on potential synergism between lipopolysaccharides (LPS) and IFNγ signaling in cells from the vasculature. Cultured human microvascular endothelial cells (HMECs) exposed to LPS activated STAT1 in a delayed manner that was inhibited by cycloheximide treatment. Pretreatment of HMECs as well as primary vascular smooth muscle cells (VSMCs) with IFNγ followed by LPS resulted in a significant increase in STAT1 phosphorylation compared with both factors alone. Increased STAT1 protein levels, strictly mediated by IFNγ, correlated with the augmented STAT1 phosphorylation that was absent in TLR4(-/-) cells. As assessed by PCR, Western analysis, and ELISA, this coincided with increased expression of the chemokine interferon gamma-induced protein 10 kDa (IP-10) and the adhesion molecule ICAM-1 in a TLR4-dependent manner.The STAT1-inhibitor fludarabine markedly reduced these effects as well as IFNγ and LPS-dependent adhesion of U937 cells to endothelial cells, emphasizing the potential importance of STAT1 in the integration of both signals. With the established roles of IFNγ and TLRs in atherosclerotic pathology, the STAT1-dependent signal integration between IFNγ and TLR in ECs and VSMCs in response to exogenous and endogenous atherogenic ligands could result in amplification of pro-inflammatory responses in the damaged vessel and be a novel mechanism involved in the initiation and progression of atherosclerosis.

STAT1 and IRF8 in Vascular Inflammation and Cardiovascular Disease: Diagnostic and Therapeutic Potential.

Inflammation importantly contributes to the pathophysiology of Cardiovascular Disease (CVD). Signal Transducer and Activator of Transcription (STAT)1 operates at the frontier of innate and adaptive immunity and its involvement in CVD has been widely appreciated. A unique role of STAT1 in cross-talk between the pro-inflammatory cytokine IFNγ and TLR4 activators (TLR4-A) has been uncovered in immune as well as vascular cells increasing inflammation. Interferon Regulatory Factor (IRF)8 whose expression was initially identified in immune cells, controls development and differentiation in close connection with PU.1. In addition, as a STAT1-target, IRF8 accounts for "immune cell-specific" STAT1-dependent functions of IFNγ and LPS. Novel studies prove that also in endothelial cells (ECs) and vascular smooth muscle cells (VSMCs), STAT1 and IRF8 orchestrate a transcriptional platform for cross-talk between IFNγ and TLR4-A, which leads to amplified pro-atherogenic responses in the vasculature. In addition to its known immune cell functions, this points to a novel "inflammation-dependent" role of IRF8 in vascular cells. In this review we present a summary of these findings and postulate STAT1- and IRF8-target genes as promising markers of vascular inflammation, and STAT1 and IRF8 as potential targets for the development of new immunosuppressive and anti-inflammatory agents for the treatment of CVD.

Reduction of Amyloid-ß Plasma Levels by Hemodialysis: An Anti-Amyloid Treatment Strategy?

BACKGROUND: Cognitive impairment in hemodialysis patients is common, but the underlying pathogenesis remains unclear. Alzheimer's disease is the most common cause of dementia in the general elderly population. Histopathological hallmarks are, among others, senile plaques, which consist of amyloid-ß (Aß). OBJECTIVE: To measure plasma levels of Aß42 and Aß40 during hemodialysis and to examine potential associations with cognitive performance in cognitively impaired hemodialysis patients. METHODS: Plasma samples of 26 hemodialysis patients were collected shortly before, after 50% of dialysis time, and at the end of a dialysis session. Aß42 and Aß40 levels were measured by a high-sensitivity ELISA for human amyloid-ß. Cognition was tested under standardized conditions using the Montreal Cognitive Assessment (MoCA) as proposed previously. RESULTS: Clearance rates of both peptides during one dialysis session were 22% and 35% for Aß42 and Aß40, respectively. Aß42 but not Aß40 baseline levels were significantly associated with MoCA test results (r = 0.654, p = 0.001). CONCLUSION: In cognitively impaired hemodialysis patients plasma Aß42 levels were associated with cognitive performance and both Aß42 and Aß40 plasma levels could be effectively reduced by dialysis. By inducing peripheral Aß sink, hemodialysis may be considered as an anti-amyloid treatment strategy.

Damage-associated molecular pattern activated Toll-like receptor 4 signalling modulates blood pressure in L-NAME-induced hypertension.

AIMS: Recent publications have shed new light on the role of the adaptive and innate immune system in the pathogenesis of hypertension. However, there are limited data whether receptors of the innate immune system may influence blood pressure. Toll-like receptor 4 (TLR4), a pattern recognition receptor, is a key component of the innate immune system, which is activated by exogenous and endogenous ligands. Hypertension is associated with end-organ damage and thus might lead to the release of damage-associated molecular patterns (DAMPs), which are endogenous activators of TLR4 receptors. The present study aimed to elucidate whether TLR4 signalling is able to modulate vascular contractility in an experimental model of hypertension thus contributing to blood pressure regulation. METHODS AND RESULTS: NG-nitro-l-arginine methyl ester (l-NAME)-induced hypertension was blunted in TLR4(-/-) when compared with wild-type mice. Treatment with l-NAME was associated with a release of DAMPs, leading to reactive oxygen species production of smooth muscle cells in a TLR4-dependent manner. As oxidative stress leads to an impaired function of the NO-sGC-cyclic GMP (cGMP) pathway, we were able to demonstrate that TLR4(-/-) was protected from sGC inactivation. Consequently, arterial contractility was reduced in TLR4(-/-). CONCLUSIONS: Cell damage-associated TLR4 signalling might act as a direct mediator of vascular contractility providing a molecular link between inflammation and hypertension.

STAT1-dependent signal integration between IFNγ and TLR4 in vascular cells reflect pro-atherogenic responses in human atherosclerosis.

Signal integration between IFNγ and TLRs in immune cells has been associated with the host defense against pathogens and injury, with a predominant role of STAT1. We hypothesize that STAT1-dependent transcriptional changes in vascular cells involved in cross-talk between IFNγ and TLR4, reflect pro-atherogenic responses in human atherosclerosis. Genome-wide investigation identified a set of STAT1-dependent genes that were synergistically affected by interactions between IFNγ and TLR4 in VSMCs. These included the chemokines Cxcl9, Ccl12, Ccl8, Ccrl2, Cxcl10 and Ccl5, adhesion molecules Cd40, Cd74, and antiviral and antibacterial genes Rsad2, Mx1, Oasl1, Gbp5, Nos2, Batf2 and Tnfrsf11a. Among the amplified genes was also Irf8, of which Ccl5 was subsequently identified as a new pro-inflammatory target in VSMCs and ECs. Promoter analysis predicted transcriptional cooperation between STAT1, IRF1, IRF8 and NFκB, with the novel role of IRF8 providing an additional layer to the overall complexity. The synergistic interactions between IFNγ and TLR4 also resulted in increased T-cell migration and impaired aortic contractility in a STAT1-dependent manner. Expression of the chemokines CXCL9 and CXCL10 correlated with STAT1 phosphorylation in vascular cells in plaques from human carotid arteries. Moreover, using data mining of human plaque transcriptomes, expression of a selection of these STAT1-dependent pro-atherogenic genes was found to be increased in coronary artery disease (CAD) and carotid atherosclerosis. Our study provides evidence to suggest that in ECs and VSMCs STAT1 orchestrates a platform for cross-talk between IFNγ and TLR4, and identifies a STAT1-dependent gene signature that reflects a pro-atherogenic state in human atherosclerosis.

STAT1 as a central mediator of IFNγ and TLR4 signal integration in vascular dysfunction.

Atherosclerosis is characterized by early endothelial dysfunction and altered vascular smooth muscle cells (VSMCs) contractility. The forming atheroma is a site of excessive production of cytokines and inflammatory ligands by various cell types that mediate inflammation and immune responses. Key factors contributing to early stages of plaque development are IFNγ and TLR4. This review provides insight in the differential STAT1-dependent signal integration between IFNγ and TLR4 signals in vascular cells and atheroma interacting immune cells. This results in increased leukocyte attraction and adhesion and VSMC proliferation and migration, which are important characteristics of EC dysfunction and early triggers of atherosclerosis.

Immunosuppression with 4SC-101, a novel inhibitor of dihydroorotate dehydrogenase, in a rat model of renal transplantation.

BACKGROUND: 4SC-101 is a novel dihydroorotate dehydrogenase inhibitor and a blocker of interleukin (IL)-17 secretion with beneficial effects in experimental lupus and inflammatory bowel disease. Its immunomodulatory effect on acute kidney rejection is not known; therefore, in this study, the impact of 4SC-101 was examined in a rat model of acute kidney rejection. METHODS: The kidneys of Brown-Norway rats were orthotopically transplanted into bilaterally nephrectomized Lewis recipients. Allograft recipients were administered with 4SC-101 at dosages of 4, 20, or 60 mg/kg per day, and survival was assessed. In the second setting, the animals were harvested 3 or 5 days after transplantation (Tx), and graft histologic diagnosis was determined. The effects of 4SC-101 on impaired renal function were examined in a model of 5/6 nephrectomy in Lewis rats. RESULTS: The recipients treated with 20-mg/kg 4SC-101 showed prolonged survival compared with placebo-treated animals (mean±SEM, 24±9.3 vs. 5.4±3 days), paralleled by less severe histologic features of acute kidney rejection such as interstitial/perivascular infiltration and tubulitis 3 and 5 days after Tx, and a lower level of IL-17 messenger RNA 5 days after Tx compared with the placebo-treated animals. In the 5/6 nephrectomy model, 20-mg/kg 4SC-101 reduced proteinuria, glomerulosclerosis, and fibrosis with decreased IL-17 messenger RNA expression. CONCLUSIONS: 4SC-101 prolongs survival after Tx, paralleled by amelioration of histologic signs of acute rejection. Furthermore, it showed no worsening effects on kidney function in a remnant kidney model and even slowed the progression of proteinuria and kidney fibrosis. Therefore, 4SC-101 might be a promising pharmaceutical agent in Tx medicine for further investigations.